This invention relates to a method of producing an electrochromic display device and more particularly to the improvement in the method of forming the electrochromic layer of such a display device.
Transition metal compounds such as tungsten oxide are known as materials exhibiting electrochromism and electrochromic display devices utilizing the electrochromism have been developed. In general, such a display device is constructed such that an electrochromic layer and an ionic conductor or electrolyte layer are sandwiched between a pair of mutually facing electrode substrates at least one of which is transparent.
For forming an electrochromic layer, it is customary to deposit a transition metal compound on an electrode substrate by means of vacuum deposition, sputtering, etc. Alternatively, powder of a transition metal compound is suitably shaped and sintered, or paste is prepared from such a powder. The sintered mass or paste of the powder is disposed between a pair of electrodes to provide an electrochromic layer.
However, the former method utilizing deposition necessitates troblesome operations and a costly apparatus for forming an electrochromic layer about 0.1 to 10 .mu.m thick uniformly over a large area and, thus, is not economical. On the other hand, it is difficult to form a uniform electrochromic layer over a large area by employing the latter method. Thus, an electrochromic display device comprising a electrochromic layer formed by the latter method tends to be unsatisfactory in the contrast of the displayed pattern.